Chemically amplified positive resist compositions are materials for the formation of patterns on a substrate by generating an acid in the exposed area upon irradiation with radiation such as far ultraviolet rays, and differentiating a solubility in a developer between the exposed area and unexposed area by the reaction using the acid as a catalyst.
Since the compositions are mainly composed of a resin having as a basic skeleton, poly(hydroxystyrene) exhibiting small absorption in a region of 248 nm, good patterns with high sensitivity and high resolution are formed, when a KrF excimer laser is used as a light source for exposure. The compositions are therefore superior to conventional naphthoquinonediazide/novolac resin-based resist compositions.
When a shorter wavelength, e.g., ArF excimer laser (193 nm) is used as a light source for exposure, on the other hand, since an aromatic group-containing compound essentially exhibits large absorption in a region of 193 nm, the above-described chemically amplified compositions are still insufficient.
In J. Vac. Sci. Technol., B9, 3357(1991), the use of poly(meth)acrylate as a polymer exhibiting small absorption in a wavelength range of 193 nm is described. The polymer is, however, accompanied with such a drawback as inferiority in the resistance to dry etching adopted ordinarily in a semiconductor production process to conventional aromatic group-containing phenolic resins.
A mixed acid generator of a specific sulfonium salt (an anion having 1 to 15 carbon atoms) and a triarylsulfonium salt is described in Japanese Patent Laid-Open No. 2000-292917, a combination of a triphenylsulfonium salt of a perfluoroalkanesulfonic acid having 4 to 8 carbon atoms and a 2-alkyl-2-adamantyl (meth)acrylate described in Japanese Patent Laid-Open No. 2000-275845, and a mixed acid generator of a specific sulfonium salt (an anion having 4 to 8 carbon atoms) and a triphenylsulfonium salt or iodonium salt of a perfluoroalkanesulfonic acid having 4 to 8 carbon atoms is described in EP1041442A.
It is the common practice to use modified illumination or a phase shift mask in order to satisfy a further miniaturization tendency of patterns. Annular illumination has been used for the formation of line and space patterns, while a halftone phase shift masks has been used for the formation of contact holes. When the halftone phase shift mask is used, however, the pattern portions are dissolved by a slight transmitted light, thereby causing a problem of sidelobe.
The p-hydroxystyrene resin using in a KrF excimer laser resist interacts with an acid generator, particularly, an ionic compound such as an onioum salt, thereby improving a solubility of the acid generator. A resin having an alicyclic hydrocarbon structure, on the other hand, does not readily cause interaction with an ionic compound such as an onium salt because of markedly high hydrophobicity so that solubility of the acid decreases. Such a resin therefore has a problem in that the resist solution tends to generate particles during storage.
In addition, conventional resist compositions are not advantageous because defocus latitude, i.e., fluctuation in line width due to defocus is accompanied.